1. Field of the Invention
The present invention relates to an optical waveguide device and a method of manufacture thereof, and more particularly to an optical waveguide device enabled to eliminate or reduce the influences of stray lights and a method of manufacture thereof.
2. Description of the Related Art
Communication technology is advancing dramatically, driven by the development of the Internet among other factors. Along with that, optical devices are required rapidly to achieve high performance and miniaturization. In order to realize this requirement, hybrid mounting of optical devices is performed briskly. One example is an optical device in which optical functional elements such as laser diodes (LDs), photodiodes (PDs) and optical amplifiers for receiving optical signals are hybrid-mounted on a planar lightwave circuit (PLC) chip.
In addition recently, in compliance with the demand for large increasing capacity in communication capacity, wavelength division multiplexing (WDM) communication is developing. For this purpose, it is frequently attempted to mount components for a plurality of channels on a single optical waveguide substrate. As an example, a plurality of light receiving elements are hybrid-mounted on an arrayed waveguide grating (AWG) as a trial production as disclosed in U.S. Pat. No. 5,680,236 (OECC2000 Tech Digest, July 2000, 12C2-2). In such hybrid mounting, optical functional elements are fixed to an end face or the top face of an optical waveguide substrate by soldering or with adhesive. As for such integrated structure, lights leaking from each part components are easy to enter into other part components as stray lights. This results in a trouble of giving rise to optical crosstalk. There are a number of known measures to prevent such optical crosstalk from increasing. For instance, where there are multiple channels, it is a general practice to expand the spacing between optical waveguides or components to be mounted in a fan-out structure.
FIG. 12 illustrates the structure of an optical device proposed to reduce optical crosstalk according to the prior art. On the optical waveguide substrate 101 of an optical waveguide device 100 are formed a plurality of optical waveguides 1021, 1022, . . . 102N. At one end of each of the optical waveguides 1021, 1022, . . . 102N is arranged a matching one of light receiving elements 1031, 1032, . . . 103N for the respective channels. Lights being inputted from the left ends of, and being transmitted in, the optical waveguides are received by the respective light receiving elements. In this proposed configuration, the spacing between the optical waveguides 1021, 1022, . . . 102N is radially expanded as they approach the light receiving elements 1031, 1032, . . . 103N. This arrangement makes it possible to expand the spacing between the light receiving elements 1031, 1032, . . . 103N. As a result, stray lights from the optical waveguides having failed to be inputted into the light receiving elements can be prevented from being inputted into light receiving elements of other channels, and optical crosstalk can be thereby reduced. However, the structure according to the prior art shown in FIG. 12 has its own problem that the optical waveguide substrate has to be enlarged with an increase in the number of channels because the mounting width of light receiving elements expands. For this reason, the number of optical waveguide substrates that can be cut out of a wafer is reduced, and the cost is accordingly increased. There is another problem that the package to mount this optical waveguide substrate cannot be miniaturized.
Also, as shown in FIG. 12, it is often impossible to achieve a sufficient effect by simply expanding the spacing between components.